This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to 9704085-1 filed in Sweden on Nov. 7, 1997; the entire content of which is hereby incorporated by reference.
This invention relates to a method and device for registering PLMNs, and relates particularly to a method and device for enhancing the list of rejected PLMNs.
A Public Land Mobile Network (PLMN) is a geographic area served by a network operator and is defined as the area in which an operator offers radio coverage and possibility to access the network A number of PLMNs are operated by different companies. The mobile terminal can be moved around, i.e. roaming, in the area which is covered by the home PLMN to which the terminal belongs. Roaming to a visited PLMN is not allowed unless the operators of the visited PLMN and the home PLMN have made agreements on that account. If roaming is not allowed the mobile station is rejected from the visited PLMN. To prevent mobile stations from making repeated attempts to register on PLMNs where roaming is not allowed, the GSM specifications have defined a specific handling when a xe2x80x9croaming rejectionxe2x80x9d is received from a visited PLMN.
Each GSM mobile terminal is provided with a SIM card (SIM=Subscriber Identity Module) which identifies the set. The SIM card belongs to the telephone subscription. It can be used in any GSM terminal. The charge for the subscription is connected to the SIM card
The specifications define that the SIM card shall contain a list that may contain up to four PLMN identities in a non-volatile memory. When a roaming rejection is received from a PLMN, the identity of that visited PLMN is Written into the list. If the list already has four PLMN identities, the oldest is removed from the list. The processor in the mobile equipment (ME), the terminal, will not automatically make registrations on PLMNs provided in the list in the SIM card. The size of the list was chosen to suit the situation for GSM (Global System for Mobile Communication) operating at the 900 MHz frequency range and DCS (Digital Cellular System) operating at the 1800 MHz frequency range where two or three operators were operating in each frequency band in each country.
In a situation where five of more PLMNs not allowing registration exist, and the home PLMN or a visited PLMN which could allow registration does not exist, or is received with a very low signal, so that the terminal will not lock to it or rather lock to a PLMN having stronger signals, the reaction of the mobile terminal is to cyclically attempt registration on networks that reject the mobile terminal. The reason for this behaviour is that the oldest failed visited PLMN has been removed from the list when a new non-allowable PLMN is inserted in the list and hence then has become available for attempts to registration again. The result is that no service is given to the user, and that registration load on the networks as well as power consumption in the mobile terminal are increased. Situations when more than to PLMNs which do not allow registration are more likely to occur when dual band mobile terminals covering both the 900 Mhz and the 1800 MHz frequency band are introduced
A natural solution to the problem stated above could be to increase the size of the non-volatile list on the SIM. However, this requires that the SIMS are modified or replaced. Another disadvantage with a large list is that an xe2x80x9coldxe2x80x9d rejection from a network is unlikely to be overwritten and the PLMN allowed to be automatically attempted again. For those users who use the automatic PLMN selection method in the mobile equipment, the networks on the list will not be available for service even if the subscriber/roaming arrangements have been changed so that a visited PLMN has been allowed after the insertion of that visited PLMN identity on the list.
Reference to GSM specification specifying the xe2x80x9clist of forbidden PLMNsxe2x80x9d is specified in the following Specifications:
-TS GSM 02.11 Ch 3.2.2.4
-TS GSM 02.17 Ch 6.1
-TS GSM 03.22 Ch 3.1
-TS GSM 04.08 Ch 4.2 and 4.4
-TS GSM 11.11 Ch 10.3.16
An object of the invention is to provide a system able to expand the list of non-allowable PLMNs which is provided in mobile terminals nowadays but in such a way that the problems of having a very long list are avoided.
Another object of the invention is to provide means to allow non-allowable PLMNs listed on the list to disappear from it in a simple, and preferably automatic way.
Still another object of the invention is to provide means to enhance the already existing list function without interfering with it.
Yet another object of the invention is to make the mobile terminal to insert a non-allowable PLMN, or at least attempt insertion, on the list only once at least within a certain time, thus to prevent a mobile terminal to repeatedly try to lock on PLMNs providing roaming rejection.
These objects are achieved by a method, and a device according to exemplary embodiments of the present invention.
The invention relates to a development of a method and a device for avoiding repeated registration attempts to register on PLMNs which do not allow registration for a mobile terminal and yet be able to attempt to register on PLMNs earlier inserted on a list of a number of identities of rejected PLMNs in a storage in the terminal but which may allow registration at a later time. The invention is characterized by providing at least a part of the list erasable to be erased at intervals; transferring surplus identities of rejected PLMNs on a non-volatile part of the list to the erasable part of the list.
Erasable part of the list are preferably erased when the mobile terminal is switched off. When a non-volatile list of registered PLMNs is provided on a SIM card in the mobile terminal, the erasable part of the list could be provided in a volatile storage connected to a computer in the mobile terminal. Each identity outputted from the non-volatile PLMNs card list when a new rejected PLMNs is registered could be transferred to the volatile storage list. The erasable part of the list should be erased when the SIM card is removed from the mobile terminal, when the terminal is switched off at a manual command and/or automatically according to predetermined conditions. Each automatic erasing could for instance occur a predetermined time after that the erasable list part is made writable again after an erase, whether the erase depended on a switch off or an automatic erase.
An arbitrary identity of a PLMN on the erasable part of the list could for instance be transferred to the non-erasable part of the list at manual control, i.e. erase the PLMN in question from the erasable part of the list and insert it on the non-erasable part of the list.
The additional list could be placed in the mobile equipment which means that the SIM card need not be changed. The solution according to the invention can be combined with an increase of the number of entries on the list of rejected PLMNs in the SIM card.